Method of fibrillating oriented film



20, 8 P. E. WILKINS 3,397,825

METHOD OF FIBRILLATING ORIENTED FILM Filed March 7, 1966 INVENTOR P. E, WILKINS By v A T TORNE Y5 United States Patent 3,397,825 METHOD OF FIBRILLATING ORIENTED FILM Paul E. Wilkins, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Mar. 7, 1966, Ser. No. 532,250 9 Claims. (Cl. 225-3) This invention relates to a method and apparatus for fibrillating film.

Heretofore oriented plastic film has been fibrillated by various methods such as lateral stretching of the whole film. Some of these methods tend to fibrillate along the weakest lines in the film and sometimes tend to make a product having a large number of interconnected fibers and therefore having fuzzy or feathery appearance. Also, some of these processes are not easily adjusted and therefore do not readily accommodate the fibrillation of films whose thickness varies from point to point in the film.

It has now been found that by resiliently supporting the film in the area where it is to be fibrillated and then impinging hard, smooth particles against the film in this area sharp, clean, and less fuzzy fibrillation occurs thereby producing a more shiny, lustrous, and neater appearing fibrillated product. Also, random splitting of the film is accomplished, as opposed to splitting following pronounced lines of weakness in the film. Further, this method of fibrillation is sufiiciently flexible to be altered during a continuous operation to accommodate various thicknesses of the film being fibrillated. Another advantage of this invention is that selected portions of the film can be shielded from the particles in various Ways, e.g., using a moving or stationary shield between the particle source and the film, so that a design can be made in the final product. The resilient support may also be varied in resiliency to vary the pattern.

Accordingly, it is an object of this invention to provide a new and improved method for fibrillation.

Other aspects, objects, and the several advantages of this invention will be apparent to those skilled in the art from the description, drawing, and appended claims.

The drawing shows an embodiment for carrying out this invention.

In the drawing there is shown a closure 1 having a conventional sandblasting nozzle 2 mounted in the top portion thereof. Closure 1 has a particle receiving zone 3 in the bottom thereof which is connected by pipe 4 to nozzle 2 so that the particles can be removed from zone 3 through pipe 4 and introduced into nozzle 2 by the vacuum action of a fluid passing through nozzle 2 in the direction of arrow 5. In the interior of zone 1 there is rotatably mounted a rubber covered drum 6. On either side of drum 6 are carried a pair of nip rolls 7 and 8. These nip rolls are employed to tension the film therebetween while it passes over roll 6. The film to be fibrillated 9 is passed from feed roll 10 in the direction of arrow 11 between both sets of nip rolls and over roll 6. The fibrillated product is collected on take-up roll 12.

The means for resiliently supporting the film in the area where it is being fibrillated can be any suitable apparatus in lieu of roll 6, e.g., a series of smaller rolls, a stationary roll, a flat stationary surface, and the like. The resilient supporting means can be formed from or coated with a suitable resilient material such as rubber, a rubbery plastic, and the like, a primary requirement being that the resilient material yield somewhat to the impact force of the particles when impinging thereon but not yield sufficiently to allow the impinging particles to penetrate through the film itself. The impinging particle therefore, due to its smooth contours, does not cut the film but rather holds that portion of the film with which it is in contact against the resilient roll 6. After initial impact, the resilient roll 6 gives somewhat to the impacting force 3,397,825 Patented Aug. 20, 1968 "ice of the particle and the film is then locally lateral stretched in the area where the film and the particle are in contact. Thus, fibrillation takes place randomly at each area of contact between a particle and the film by first, the holding action caused by the initial impact of the particle on the film, and second, the subsequent lateral stretching caused by the slight deflection of the resilient supporting surface after the initial impact of the particle.

Generally, any orientable plastic film can be employed in this process. The film can be in a uniaxially, biaxially, or other multiaxially oriented condition. The film can be oriented in any conventional manner well known to those skilled in the art including cooling the film to crystallize it and then orienting same by stretching and the like or heating the film to a temperature below that at which the film is in the molten state and then stretching same. By orientation, what is generally meant to be covered is deforming, e.g., stretching the film below that temperature at which the film is substantially in the molten state, to thereby increase the strength of the film at least in the direction in which it is deformed.

Generally, films of l-olefins having from 2 to 8 carbon atoms per molecule which have been oriented by stretching before or during fibrillation in primarily one direction so that the film after stretching is at least 3 times longer than it was before stretching, i.e., 3 to 1, can be used. When film of polyethylene which has a density of at least about 0.94 gram per cubic centimeter is employed the ratio of length in the stretched direction to original length should be at least 4 to 1 and when polypropylene is employed this ratio should be at least 6 to 1. Polymers of l-olefins can be made in any conventional manner. A particularly suitable method is that disclosed in US. Patent 2,853,741. The film can be made from the polymers in any conventional manner such as by extrusion, casting, flattening blown tubing, and the like.

Other conventional plastic films that can be employed in this invention include blends and copolymers of l-olefins as above-described with each other and with other polymers such as polyamides, polyesters, polyvinyl alcohol, acrylic polymers, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, and the like. Of course, homopolymers of the l-olefins and other materials described can also be employed as well as copolymers. A stretch or orientation ratio of at least 3 to 1 can also be employed with these plastic films.

The film can be of any length and width and substantially any thickness, the minimum thickness of the film being that which will produce a substantially self-sustaining film and the maximum thickness being dictated by the fibrillation capability of the apparatus employed. Preferably, the thickness of the film will vary from that which is suflicient to form a substantially self-sustaining film, e.g., /2 mil, to about 6 mils. Thicker films can be treated by using heavier duty apparatus, larger particles, and the like. Repeated passes past the same apparatus can be employed to more thoroughly fibrillate film or to effectively fibrillate thicker and/or tougher films with lighter apparatus. The method of this invention can also be adjusted so that fibrillation of the film does not take place but in eifect impingement of the particles on the film acts as a pretreatment for subsequent conventional splitting such as stretching the film between two elastomeric materials, and the like.

The particulate material employed can be any relatively hard material which is capable of being formed into smooth surfaced, preferably round, particles. The particles have smooth surfaces to effect localized stretching of the film and thereby cause fibrillation as opposed to sharp particles which would have a cutting effect. Examples of suitable materials include round sand or rock particles, metal spheres, polymer spheres, and the like. The'size of the particles can vary widely, the minimum dimension being substantially the thickness of the film to be treated and the maximum dimension not exceeding preferably A3, inch. I

The particles can be motivated at least in part by a carrier fluid which can be liquid, e.g., water and the like, or gaseous, e.g., air, nitrogen and the like. Gaseous carriers are presently preferred and the pressure with which the carrier is forced against the film will vary widely depending upon the particles, the carrier, the film, and the like. Generally, the pressure will be at least 50 p.s.i.g. although the pressure will desirably be that which is sufficient to effect fibrillation of the film and will generally be in the range of from 75 to about 1000 p.s.i.g., lesser and greater pressures being useful if fibrillation can be effected thereby. In certain embodiments of the invention the pressure of the fluid is dictated in part by the use of the fluid to pull particles from their source into the dispersing nozzle for impingement on the film as shown in the drawing. Dispersing devices such as nozzles can be employed so that the particles are forced upwardly, downwardly, or at any desired angle against the film. The film can be passed by the particle dispersing apparatus at generally any spacing therefrom which can vary from 1 or less inches to 12 or more inches from the outlet nozzle of the dispersing apparatus. The rate at which the film is passed by the article dispersing apparatus will vary widely and can be any rate at which fibrillation is effected.

The angle of impingement of the particles on the film can vary from a very acute angle relative to the flat surface of the film, e.g., on the order of to a right angle with respect to the film surface, the right angle being presently preferred.

The film can be either exposed directly to the particles or a separate resilient film or sheet of material which can be formed of rubber, rubbery plastic, and the like may be interposed between the film to be fibrillated and the source of the impinging particles, thereby protecting the surface of the film to be fibrillated from direct contact with these particles.

The propelling force of the particles can be supplied by means other than the fluid under pressure. For example, the particles can be simply dropped from an adequate height onto the film, or rolled down an incline against the film, or by feeding the particles to the center of a centrifugal shot peening wheel and directing the particles forced from that wheel against the film, and the like.

EXAMPLE A film composed of a homopolymer of propylene and about 11 inches wide was oriented by stretching the film at a temperature of 230 F. until the length in the stretched direction was 12.4 times that of the unstretched length. The oriented film had a width of about 3 inches and a thickness of about 4 mils.

The film at room temperature was then passed through an apparatus substantially the same as that shown in the drawing wherein a plurality of No. 330 (0.05 inch diameter) chilled steel shot was impinged on the film by an air stream passing through nozzle 2 which air stream was under a pressure of about p.s.i.g. at the nozzle inlet connection. The film was passed through the closure 1 at a speed of about 3 feet per minute and a distance from the outlet of nozzle 2 that was varied from 4 to 12 inches.

Fibrillation readily occurred and the fibrillated product was a cleanly and uniformly split, nonwoven fabric.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope thereof.

I claim:

1. In a method for fibrillating an oriented plastic film, the improvement comprising resiliently supporting the film in the area where it is to be fibrillated, and impinging hard, smooth surfaced particles against said film in said supported area so that substantial yielding of the film to the impact force of the particles is prevented, the impact force of said particles being suflicient to cause fibrillation of said film.

2. The method according to claim 1 wherein said film is composed of at least one of oriented homopolymers and/ or copolymers and/ or blends thereof of l-olefins having from 2 to 8 carbon atoms per molecule, inclusive, and polyamides and the film is oriented so that the oriented length is at least 3 times the unoriented length.

3. The method according to claim 1 wherein said particles are substantially spherical.

4. The method according to claim 1 wherein said particles have a maximum dimension not greater than inch.

5. The method according to claim 1 wherein the resilient means supporting the film is sufficient to allow the impinging particles to deflect the film but insufficient to allow said particles to pass through the thickness of said film.

6. The method according to claim 1 wherein said film is passed through a substantially closed zone and over a rotatable resilient means in said zone, the particles are impinged upon said film as it passes over said resilient supporting means.

7. The method according to claim 1 wherein said par ticles are at least in part carried by a supporting fluid.

8. The method according to claim 1 wherein the film is polyethylene, and the particles are metal spheres having a maximum diameter no greater than A; inch.

9. The method according to claim 1 wherein the film is polypropylene, an air carrier fluid under pressure of at least 50 p.s.i.g. is employed to carry and motivate the particles, and the particles are steel balls having a maximum diameter no greater than /8 inch.

References Cited UNITED STATES PATENTS 3,242,035 3/1966 White 281.4 X

JAMES M. MEISTER, Primary Examiner. 

1. IN A METHOD FOR FIBRILLATING AN ORIENTED PLASTIC FILM, THE IMPROVEMENT COMPRISING A RESILIENTLY SUPPORTING THE FILM IN THE AREA WHERE IT IS TO BE FIBRILLATED, AND IMPRINGING HARD, SMOOTH SURFACED PARTICLES AGAINST SAID FILM IN SAID SUPPORTED AREA SO THAT SUBSTANTIAL YIELDING OF THE FILM TO THE IMPACT FORCE OF THE PARTICLES IS PREVENTED, THE IMPACT FORCE OF SAID PARTICLES BEING SUFFICIENT TO CAUSE FIBRILLATION OF SAID FILM. 